Magnetization transfer imaging is based on the exchange of magnetization in biologic tissues between a pool of protons in water and a pool of protons that is bound to macromolecules. The magnitude of the effect depends, in part, on the ratio of water and macromolecules. Magnetization exchange processes can involve a pool of protons characterized by different chemical shifts.
In the brain, macromolecules that contribute to the magnetization transfer effect include the cholesterol component of myelin, cerebrosides, and phospholipids.
Currently available protocols for magnetization transfer (MT) imaging and off-resonance experiments (such as off-resonance rotating frame T1ρ or Z-spectroscopy) are inadequate. For example, estimation of magnetization transfer (MT) parameters in vivo can be compromised by an inability to drive the magnetization to a steady state using allowable levels of radio frequency (RF) irradiation, due to safety concerns (tissue heating and specific absorption rate (SAR)).